Integrated Circuit (IC) is a product made by an integration of high-technologies such is as the precision machinery, the microelectronics, the computer technology, the control technology, the laser technology and the precision measurement technology. Lithography Technology is one of the most critical factors in the IC manufacturing process and is a very complex process. In simple terms, Lithography Technology can include the following nine steps: vapor prime processing, spin coating, soft baking, alignment, exposure, post-exposure baking, developing, hard baking, and after developing inspection. Among them, the exposure is a critical technology step.
Since the development of semiconductor technology, the lithography has experienced the development process: the contact lithography, the proximity lithography, the scanning projection lithography, and the currently widely used step-and-scan lithography. The step-and-scan lithography is a forefront technology for the IC lithography processing. The step-and-scan lithography projects, via a reduction imaging optical system, which transfer a pattern on a reticle mask onto a single exposure shot (the exposing region on a wafer may be divided into multiple exposure shots, and an exposure shot may include one or more chips on the wafer) of a wafer coated with photoresist, by the synchronous motion of a reticle stage and a wafer stage. After one exposure shot is scanned and exposed, the wafer stage is stepped to another exposure shot and the action of scanning and exposing is repeated. This continues until all the exposure shots on the wafer are scanned and exposed. Then a pattern with a reduced scale is finally duplicated onto the wafer after processes such as shaping and developing. That is to say, the scanning and exposing process for the whole wafer includes two alternately circulated motions: a stepping motion, and a scanning and exposing motion. When a wafer stage is stepped into an exposure shot, the wafer stage and the reticle stage perform the synchronous scanning and exposing process for the exposure shot; and then the wafer stage is stepped into another exposure shot and the synchronous scanning and exposing process is repeated.
FIG. 1 is a diagram of speed curves of a wafer stage and a reticle stage during a scanning and exposing motion of a single exposure shot on a wafer. As shown in FIG. 1, the scanning and exposing motion of a single exposure shot on a wafer may be divided into three obvious stages, namely a starting stage (including an acceleration stage and a stabilizing stage), a scanning and exposing stage (a uniform-speed stage) and an ending stage (a deceleration stage). Firstly, the wafer stage and the reticle stage begin to accelerate from a is stationary state. After the acceleration for a period of time tac, the speed of the wafer stage reaches Vw and the speed of the reticle stage reaches Vr (it is assumed that the size of the pattern on the reticle mask is 4 times as big as the size of a pattern finally formed on the wafer, namely 4Vw=Vr). After stabilizing for a period of time tst, the wafer stage and the reticle stage begin to scan and expose at a uniform speed. After scanning and exposing for a period of time tsc, the wafer stage and the reticle stage begin to decelerate. After decelerating for a period of time tde, the speeds of the wafer stage and the reticle stage are decreased to zero.
As can be seen from above, during the scanning and exposing motion of a single exposure shot, the exposure shot may be scanned and exposed only when the speeds of the wafer stage and the wafer stage actually reach the uniform speed. In other words, during the entire period of time t (t=tac+tst+tsc+tde) for scanning and exposing a single exposure shot, the exposing is effective only during the period of time ts, and the exposing is not effective during other periods of time (tac, tst, tde). That is to say only tsc is effective time and tac, tst and tde are ineffective. With the conventional techniques, the entire period of time for scanning and exposing a single exposure shot generally lasts for 0.26 s, however the period of time actually used for scanning and exposing only lasts for 0.06 s, which means that the effective period of time for scanning and exposing only accounts for about 20% while the ineffective period of time for scanning and exposing only accounts for about 80%. The ineffective period of time for scanning and exposing increases the total period of time for manufacturing a wafer and limits the production efficiency of the wafer.
Thus, there is a need to provide an improved scanning and exposing method for the lithography machine to avoid low production efficiency.